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2019-07-02 yzy86 9881 0 0  

Two specialized muscles give them a rangeof expression that wolves’ eyes lack.


Dogs, more so than almost any otherdomesticated species, are desperate for human eye contact. When raised aroundpeople, they begin fighting for our attention when they’re as young as fourweeks old. It’s hard for most people to resist a petulant flash of puppy-dogeyes—and according to a new study, that pull on the heartstrings might beexactly why dogs can give us those looks at all.


A paper published today in the Proceedingsof the National Academy of Sciences found that dogs’ faces are structured forcomplex expression in a way that wolves’ aren’t, thanks to a special pair ofmuscles framing their eyes. These muscles are responsible for that “adopt me”look that dogs can pull by raising their inner eyebrows. It’s the firstbiological evidence scientists have found that domesticated dogs might haveevolved a specialized ability used expressly to communicate better with humans.


For the study, a team at the University ofPortsmouth’s Dog Cognition Centre looked at two muscles that work together towiden and open a dog’s eyes, causing them to appear bigger, droopier, andobjectively cuter. The retractor anguli oculi lateralis muscle and the levatoranguli oculi medialis muscle (mercifully known as RAOL and LAOM) form twoshort, straight lines, which connect the ring of muscle around a dog’s eye toeither end of the brow above.


These researchers have long been interestedin the ways dogs make eye contact with humans and, in particular, how they movetheir eyebrows. In 2017, Juliane Kaminski, the lead author of the new paper,found that dogs moved their eyebrows more often while a human paid attention tothem, and less often when they were ignored or given food (which, sorry to say,is a more exciting stimulus for them than human love). That suggested themovement is to some degree voluntary. On our side of these longing glances,research has also shown that when dogs work these muscles, humans respond morepositively. And both man and mutt benefit from a jolt of oxytocin when lockedin on each other.


This isn’t simply a fortuitous love story,in which the eyes of two species just so happen to meet across a crowdedplanet. Like all the best partnerships, this one is more likely the result ofyears of evolution and growth. If dogs developed their skill for eyebrowmanipulation because of their connection to humans, one way to tell would be tolook for the same capacity in wolves. Because dogs split off from their wolfrelatives—specifically, gray wolves—as many as 33,000 years ago, studying thetwo animals is a bit like cracking open a four-legged time capsule. Divergencebetween the two species marked the start of dogs’ domestication, a longevolutionary process influenced—and often directly driven—by humans. Today,researchers can identify and study differences between the species to gain anunderstanding of exactly how dogs have changed over time.


In this case, those eyebrow-raising musclesdo appear to be an addition to dogs’ anatomy. In the four gray wolves theresearchers looked at, neither muscle was present. (They did find bundles offibers that could be the precursors to the RAOL and LAOM.) In five of the sixbreeds of dogs the researchers looked at, both muscles were fully formed andstrong; in the Siberian husky, the wolflike, oldest breed of the group, the researcherswere unable to locate a RAOL.


Sometimes, the origins of changes likethese aren’t immediately apparent. Certain physical dog traits—including floppyears and short snouts—likely originate from the same set of developmental cellsthat code for tameness, a preferable trait in household pets, for instance. Inthe case of this new research, though, the connection between the physicaltrait and the related behavior is a bit more direct. “Previous work—and much ofit by these same authors—had shown that these muscles were responsible forenhancing positive responses in humans,” Brian Hare, the director of DukeUniversity’s Canine Cognition Center and the editor of the paper, told TheAtlantic via email, “but the current suggests the origin of these facialexpressions is after dogs split from wolves.”

By evolutionary standards, the time sincethis split has been remarkably short for two new facial muscles to havedeveloped. For a species to change that quickly, a pretty powerful force mustbe acting on it. And that’s where humans come in. We connect profoundly withanimals capable of exaggerating the size and width of their eyes, which makesthem look like our own human babies and “hijacks” our nurturing instincts.Research has already demonstrated that humans prefer pets with more infantlikefacial features, and two years ago, the authors of this latest study showedthat dogs who made the facial movement enabled by the RAOL and LAOM muscles—anexpression we read as distinctly humanlike—were more likely to be selected foradoption from a shelter than those who didn’t. We might not have bred dogs forthis trait knowingly, but they gained so much from having it that it became awidespread facial feature. “These muscles evolved during domestication, but almostcertainly due to an advantage they gave dogs during interactions with humansthat we humans have been all but unaware of,” Hare explained.


“It’s such aclassically human system that we have, the ways we interact with our owninfants,” says Angie Johnston, an assistant professor at Boston College whostudies canine cognition and was not involved with the study. “A big themethat’s come out again and again in canine cognition and looking at thedomestication of dogs is that it seems like they really just kind of dove rightinto our society in the role of being an infant or a small child in a lot ofways. They’re co-opting existing systems we have.”


The same humanlike facial gestures couldalso be a dog’s way of simply securing attention in the first place. Eyebrowraising is one of the most well-understood examples of what researchers callostensive cues, a family of nonverbal signals (often facial movements andexpressions) humans send one another to convey their intention to directlycommunicate. Dogs’ uncanny ability to mimic this human expression likely leadsus to project certain human emotions onto them in ways we don’t with otheranimals, regardless of what they might actually be feeling.


The movement of the RAOL and LAOM musclesis particularly open to interpretation. “In different contexts we’ll call thatsomething different,” says Alexandra Horowitz, a senior research fellow at theBarnard College Dog Cognition Lab. “In one case, I might say it’s sad, but inanother case I’ll say, He’s really paying attention. It can look wry, like aquestioning or unbelieving look.” According to Horowitz, dogs are the onlyanimals aside from our primate cousins that are expressive in this eerilyfamiliar way. Horses alone share the ability to twist their eyes into the samedoleful shape, but their overall expressions don’t strike us as humanlike inthe same way that dogs’ do. With dogs, Horowitz points out, we’re so driven toconnect that we often search for “smiles” in the shapes of dogs’ mouths. Thenew research, she says, “makes me think it’s more about being able to move theface in a way that humans move the face. We don’t like unexpressive faces.”


Both Horowitz and Johnston suggested thatsimilar studies looking at populations of dingoes (which Johnston researches)and Siberian foxes could provide yet another time capsule of sorts forunderstanding eyebrow movements and other evolutionary traits. Both specieslive near humans and are some of the closest living relatives to the earliestdogs. Why did they stay wild while dogs drifted into domestication? “Anythingto do with getting to the bottom of why we as a species picked out this oneanimal can carry a huge amount of information,” Horowitz says. “In some ways,it’s discovering something about ourselves.”



1、Meanwhile, catsstill don’t give a fuck.


2、"It’s the firstbiological evidence scientists have found that domesticated dogs might haveevolved a specialized ability used expressly to communicate better withhumans."
I don't think this has anything to do withevolution at all. While dogs may use these traits to their advantage, it ishumans that are ultimately breeding the traits that they consider mostappealing.


3、Well wouldn't thatstill be evolution through artificial selection?


4、Yeah, that's myimpression. If humans had already befriended dogs, developing new facialmuscles would seem to offer little evolutionary advantage.


5、Not a surprise.We've turned wolves into some pretty horrendously inbred creatures. The fullbred ones, at least.


6、That was superinteresting! Thanks!